[PATCH 8/8] [gdb/symtab] Support .debug_line with DW_FORM_line_strp
Tom de Vries
tdevries@suse.de
Mon Oct 25 10:30:00 GMT 2021
I noticed a new gcc option -gdwarf64 and tried it out (using gcc 11.2.1).
With a test-case hello.c:
...
int
main (void)
{
printf ("hello\n");
return 0;
}
...
compiled like this:
...
$ gcc -g -gdwarf64 ~/hello.c
...
I ran into:
...
$ gdb -q -batch a.out
DW_FORM_line_strp pointing outside of .debug_line_str section \
[in module a.out]
...
Debugging gdb revealed that the string offset is:
...
(gdb) up
objfile=0x182ab70, str_offset=1378684502312,
form_name=0xeae9b5 "DW_FORM_line_strp")
at src/gdb/dwarf2/section.c:208
208 error (_("%s pointing outside of %s section [in module %s]"),
(gdb) p /x str_offset
$1 = 0x14100000128
(gdb)
...
which is read when parsing a .debug_line entry at 0x1e0.
Looking with readelf at the 0x1e0 entry, we have:
...
The Directory Table (offset 0x202, lines 2, columns 1):
Entry Name
0 (indirect line string, offset: 0x128): /data/gdb_versions/devel
1 (indirect line string, offset: 0x141): /home/vries
...
which in a hexdump looks like:
...
0x00000200 1f022801 00004101 00000201 1f020f02
...
What happens is the following:
- readelf interprets the DW_FORM_line_strp reference to .debug_line_str as
a 4 byte value, and sees entries 0x00000128 and 0x00000141.
- gdb instead interprets it as an 8 byte value, and sees as first entry
0x0000014100000128, which is too big so it bails out.
AFAIU, gdb is wrong. It assumes DW_FORM_line_strp is 8 bytes on the basis
that the corresponding CU is 64-bit DWARF. However, the .debug_line
contribution has it's own initial_length field, and encodes there that it's
32-bit DWARF.
Fix this by using the correct offset size for DW_FORM_line_strp references
in .debug_line.
Note: the described test-case does trigger this complaint (both with and
without this patch):
...
$ gdb -q -batch -iex "set complaints 10" a.out
During symbol reading: intermixed 32-bit and 64-bit DWARF sections
...
The reason that the CU has 64-bit dwarf is because -gdwarf64 was passed to
gcc. The reason that the .debug_line entry has 32-bit dwarf is because that's
what gas generates. Perhaps this is complaint-worthy, but I don't think it
is wrong.
Tested on x86_64-linux, using native and target board dwarf64.exp.
---
gdb/dwarf2/line-header.c | 15 +++---
gdb/dwarf2/read.c | 12 +++++
gdb/dwarf2/read.h | 5 ++
gdb/testsuite/gdb.dwarf2/dw2-lines.exp | 22 +++++---
gdb/testsuite/lib/dwarf.exp | 75 ++++++++++++++++++++++----
5 files changed, 106 insertions(+), 23 deletions(-)
diff --git a/gdb/dwarf2/line-header.c b/gdb/dwarf2/line-header.c
index 15195764c89..852e2851e99 100644
--- a/gdb/dwarf2/line-header.c
+++ b/gdb/dwarf2/line-header.c
@@ -137,7 +137,7 @@ read_checked_initial_length_and_offset (bfd *abfd, const gdb_byte *buf,
static void
read_formatted_entries (dwarf2_per_objfile *per_objfile, bfd *abfd,
const gdb_byte **bufp, struct line_header *lh,
- const struct comp_unit_head *cu_header,
+ unsigned int offset_size,
void (*callback) (struct line_header *lh,
const char *name,
dir_index d_index,
@@ -187,9 +187,12 @@ read_formatted_entries (dwarf2_per_objfile *per_objfile, bfd *abfd,
break;
case DW_FORM_line_strp:
- string.emplace
- (per_objfile->read_line_string (buf, cu_header, &bytes_read));
- buf += bytes_read;
+ {
+ const char *str
+ = per_objfile->read_line_string (buf, offset_size);
+ string.emplace (str);
+ buf += offset_size;
+ }
break;
case DW_FORM_data1:
@@ -372,7 +375,7 @@ dwarf_decode_line_header (sect_offset sect_off, bool is_dwz,
{
/* Read directory table. */
read_formatted_entries (per_objfile, abfd, &line_ptr, lh.get (),
- cu_header,
+ offset_size,
[] (struct line_header *header, const char *name,
dir_index d_index, unsigned int mod_time,
unsigned int length)
@@ -382,7 +385,7 @@ dwarf_decode_line_header (sect_offset sect_off, bool is_dwz,
/* Read file name table. */
read_formatted_entries (per_objfile, abfd, &line_ptr, lh.get (),
- cu_header,
+ offset_size,
[] (struct line_header *header, const char *name,
dir_index d_index, unsigned int mod_time,
unsigned int length)
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index e456c37e193..a807f90568f 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -20286,6 +20286,18 @@ read_indirect_string (dwarf2_per_objfile *per_objfile, bfd *abfd,
/* See read.h. */
+const char *
+dwarf2_per_objfile::read_line_string (const gdb_byte *buf,
+ unsigned int offset_size)
+{
+ bfd *abfd = objfile->obfd;
+ ULONGEST str_offset = read_offset (abfd, buf, offset_size);
+
+ return per_bfd->line_str.read_string (objfile, str_offset, "DW_FORM_line_strp");
+}
+
+/* See read.h. */
+
const char *
dwarf2_per_objfile::read_line_string (const gdb_byte *buf,
const struct comp_unit_head *cu_header,
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 1638d8521c0..fe34e3f95ae 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -517,6 +517,11 @@ struct dwarf2_per_objfile
const struct comp_unit_head *cu_header,
unsigned int *bytes_read_ptr);
+ /* Return pointer to string at .debug_line_str offset as read from BUF.
+ The offset_size is OFFSET_SIZE. */
+ const char *read_line_string (const gdb_byte *buf,
+ unsigned int offset_size);
+
/* Return true if the symtab corresponding to PER_CU has been set,
false otherwise. */
bool symtab_set_p (const dwarf2_per_cu_data *per_cu) const;
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-lines.exp b/gdb/testsuite/gdb.dwarf2/dw2-lines.exp
index 27134af8f5d..9cc24955102 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-lines.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-lines.exp
@@ -37,18 +37,19 @@ proc line_for { l } {
}
# Execute test.
-proc test_1 { _cv _cdw64 _lv _ldw64 } {
+proc test_1 { _cv _cdw64 _lv _ldw64 {_string_form ""}} {
global srcfile srcfile2 testfile
- global cv cdw64 lv ldw64
+ global cv cdw64 lv ldw64 string_form
set cv $_cv
set cdw64 $_cdw64
set lv $_lv
set ldw64 $_ldw64
+ set string_form $_string_form
set asm_file [standard_output_file $srcfile2]
Dwarf::assemble $asm_file {
declare_labels Llines
- global srcdir subdir srcfile cv cdw64 lv ldw64
+ global srcdir subdir srcfile cv cdw64 lv ldw64 string_form
global func_info_vars
foreach var $func_info_vars {
global $var
@@ -75,7 +76,7 @@ proc test_1 { _cv _cdw64 _lv _ldw64 } {
}
}
- lines [list version $lv is_64 $ldw64] Llines {
+ lines [list version $lv is_64 $ldw64 string_form $string_form] Llines {
include_dir "${srcdir}/${subdir}"
file_name "$srcfile" 1
@@ -121,12 +122,18 @@ proc test_1 { _cv _cdw64 _lv _ldw64 } {
# Add unique test prefix.
-proc test { cv cdw64 lv ldw64 } {
+proc test { cv cdw64 lv ldw64 {string_form ""}} {
with_test_prefix cv=$cv {
with_test_prefix cdw=[expr $cdw64 ? 64 : 32] {
with_test_prefix lv=$lv {
with_test_prefix ldw=[expr $ldw64 ? 64 : 32] {
- test_1 $cv $cdw64 $lv $ldw64
+ if { $string_form == "" } {
+ test_1 $cv $cdw64 $lv $ldw64
+ } else {
+ with_test_prefix string_form=$string_form {
+ test_1 $cv $cdw64 $lv $ldw64 $string_form
+ }
+ }
}
}
}
@@ -157,6 +164,7 @@ for { set cv $cv_low } { $cv <= $cv_high } { incr cv } {
foreach cdw64 { 0 1 } {
foreach ldw64 { 0 1 } {
- test 5 $cdw64 5 $ldw64
+ test 5 $cdw64 5 $ldw64 string
+ test 5 $cdw64 5 $ldw64 line_strp
}
}
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 76ba65df9fd..4e777e4cceb 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -2143,9 +2143,11 @@ namespace eval Dwarf {
variable _line_saw_program
variable _line_header_end_label
variable _line_unit_version
+ variable _line_is_64
+ variable _line_string_form
# Establish the defaults.
- set is_64 0
+ set _line_is_64 0
set _line_unit_version 4
set _unit_addr_size default
set _line_saw_program 0
@@ -2155,14 +2157,17 @@ namespace eval Dwarf {
set _line_header_finalized 0
set _default_is_stmt 1
set _seg_sel_size 0
+ #set _line_string_form string
+ set _line_string_form line_strp
foreach { name value } $options {
switch -exact -- $name {
- is_64 { set is_64 $value }
+ is_64 { set _line_is_64 $value }
version { set _line_unit_version $value }
addr_size { set _unit_addr_size $value }
seg_sel_size { set _seg_sel_size $value }
default_is_stmt { set _default_is_stmt $value }
+ string_form { set $_line_string_form $value }
default { error "unknown option $name" }
}
}
@@ -2189,7 +2194,7 @@ namespace eval Dwarf {
set header_len_label [_compute_label "line${_line_count}_header_start"]
set _line_header_end_label [_compute_label "line${_line_count}_header_end"]
- if {$is_64} {
+ if {$_line_is_64} {
_op .4byte 0xffffffff
_op .8byte "$unit_end_label - $unit_len_label" "unit_length"
} else {
@@ -2206,7 +2211,7 @@ namespace eval Dwarf {
_op .byte $_seg_sel_size "seg_sel_size"
}
- if {$is_64} {
+ if {$_line_is_64} {
_op .8byte "$_line_header_end_label - $header_len_label" "header_length"
} else {
_op .4byte "$_line_header_end_label - $header_len_label" "header_length"
@@ -2264,12 +2269,22 @@ namespace eval Dwarf {
variable _line_file_names
variable _line_unit_version
+ variable _line_is_64
+ variable _line_string_form
if { $_line_unit_version >= 5 } {
_op .byte 1 "directory_entry_format_count"
_op .uleb128 1 \
"directory_entry_format (content type code: DW_LNCT_path)"
- _op .uleb128 0x08 \
- "directory_entry_format (form: DW_FORM_string)"
+ switch $_line_string_form {
+ string {
+ _op .uleb128 0x08 \
+ "directory_entry_format (form: DW_FORM_string)"
+ }
+ line_strp {
+ _op .uleb128 0x1f \
+ "directory_entry_format (form: DW_FORM_line_strp)"
+ }
+ }
set nr_dirs [llength $_line_include_dirs]
# For entry 0.
@@ -2282,14 +2297,38 @@ namespace eval Dwarf {
[concat [list $dirname] $_line_include_dirs]
foreach dirname $_line_include_dirs {
- _op .ascii [_quote $dirname]
+ switch $_line_string_form {
+ string {
+ _op .ascii [_quote $dirname]
+ }
+ line_strp {
+ declare_labels string_ptr
+ _defer_output .debug_line_str {
+ string_ptr:
+ _op .ascii [_quote $dirname]
+ }
+ if { $_line_is_64 } {
+ _op .8byte $string_ptr
+ } else {
+ _op .4byte $string_ptr
+ }
+ }
+ }
}
_op .byte 2 "file_name_entry_format_count"
_op .uleb128 1 \
"file_name_entry_format (content type code: DW_LNCT_path)"
- _op .uleb128 0x08 \
- "file_name_entry_format (form: DW_FORM_string)"
+ switch $_line_string_form {
+ string {
+ _op .uleb128 0x08 \
+ "directory_entry_format (form: DW_FORM_string)"
+ }
+ line_strp {
+ _op .uleb128 0x1f \
+ "directory_entry_format (form: DW_FORM_line_strp)"
+ }
+ }
_op .uleb128 2 \
"file_name_entry_format (content type code: DW_LNCT_directory_index)"
_op .uleb128 0x0f \
@@ -2307,7 +2346,23 @@ namespace eval Dwarf {
[concat [list $filename $diridx] $_line_file_names]
foreach { filename diridx } $_line_file_names {
- _op .ascii [_quote $filename]
+ switch $_line_string_form {
+ string {
+ _op .ascii [_quote $filename]
+ }
+ line_strp {
+ declare_labels string_ptr
+ _defer_output .debug_line_str {
+ string_ptr:
+ _op .ascii [_quote $filename]
+ }
+ if { $_line_is_64 } {
+ _op .8byte $string_ptr
+ } else {
+ _op .4byte $string_ptr
+ }
+ }
+ }
_op .uleb128 $diridx
}
} else {
--
2.26.2
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